The invention relates to a method for centering a packing container, such as a tube in an apparatus for heating an open tube end by hot air for the subsequently welding or sealing the tube edges, as well as an apparatus for heating the edges of the filling opening of reception containers, such as tubes, by hot gas for the subsequent closing of the same, with a nozzle being introducable into the filling opening of the container end for the hot gas supply, and the opening bringing about a substantially radially outwardly directed gas discharge.
It is known to close the ends of containers, bounding filling openings and, in particular, tubes by hot air sealing or welding. Hot air is blown into the container end and heats the tube edge or rim. Subsequently the container end is compressed by the jaws of a closing station and is sealed by hot welding in a manner described, for example, in U.S. Pat. No. 4,511,426.
With an apparatus of the aforementioned type, hot air is introduced into the interior of the tube end and the latter is heated; however, their is a risk of the heated edges shrinking and of the surrounding holding or retaining ring sticking.
The aim underlying the invention essentially resides in preventing shrinking and sticking of the softened tube end on a holding or centering means.
According to the method of the present invention, the tube end is externally supplied centering gas, more particularly, air, with the apparatus of the present invention providing a contact-free centering means for the container end.
Contact-free centering is brought about in accordance with the present invention in that the container or tube end is externally supplied with air or inert gas, which does not have to be heated as opposed to the air introduced into the interior of the container end and, the externally supplied air or inert gas may be at room temperature or, for example, up to 50.degree. C., so that no thermal energy has to be supplied to the outside. Furthermore, through the supply of air up to the indicated temperature, it is ensured that the container end is only heated and softened on the inside, whereas, the outside is kept relatively cooler, so that a shrinkage of the free container end, such as can occur in the state of the art, is reliably avoided. Nevertheless by the pressing jaws and softening in the interior of the container or tube end, the tube end can be closed by welding. Simultaneously the sticking of the outside of the tube to the centering means and to the pressing jaws carrying out the closing is prevented.
The contact-free centering brought about by centering gas leads to an increased tube flow rate or throughput, without any risk of the welded tubes bursting. The inventive construction obviates complicated adjustments and leads to a high degree of reliability and long service life.
According to preferred developments, the gas is forced into an annular clearance between the outer circumference of the tube end and a boundary wall surrounding the same in spaced manner. In addition, the centering gas, supplied from the outside, is supplied at a higher pressure than the hot gas introduced into the interior of the tube end. Due to the fact that the externally supplied centering air is at a lower overpressure than the externally supplied hot air, it is reliably avoided that hot air passes over the front edge of the tube end and onto the outside thereof, where it could lead to a shrinkage or damage to the tube varnish imprint. The overpressure may be low, and, for example, the overpressure of the externally supplied centering air may be about 0.1 bar and that of the hot air only about 0.05 bar.
According to further preferred developments of the invention, the nozzle surrounding the container end is provided with substantially radially inwardly directed gas outlet, with an inner contour of the nozzle opening being slightly larger than the outer contour of the container end. In particular the centering air nozzle has a directional component directed towards the container end and at the axial height of the hot air nozzle the container end is surrounded at a limited distance by a cylindrical wall area. Normally cylindrical ends of containers, particularly tubes are closed. However, prior to welding, the ends can also have a different shape, e.g. can be oval or elliptical in cross-section. In this case, the inner contour of the outer nozzle is adapted to the corresponding outer contour of the container end and surrounds the same with a small spacing. The same applies if, in preferred manner, the container end is surrounded at the axial height of the hot air nozzle and at a limited distance by a cylindrical wall area. Such an axially parallel wall is also adapted to the contour of the container end and surrounds the same at an adequate, but small distance of, for example, 0.5 mm. Preferably the centering air nozzle is at a smaller axial distance from the closed side of the container than the hot air nozzle. As a result the centering air supplied from the outside passes over the end over an adequate area for centering purposes and in particular comes into contact with the container exterior and centering takes place below the supply plane of the hot air melting the container edge.